Because of the increasing problem of disposing of industrial and domestic wastes, there is currently substantial interest in the use of biodegradable polymers in many applications. Among the more serious of these problems is the disposal of various plastic wastes, containing polymers such as polyethylene, polypropylene, polystyrene, polyurethanes and the like. These by and large are not biodegradable, particularly after being covered, such as in a landfill. Though polymers of lactic acid and glycolic acid and several other aliphatic polyesters are known to be hydro/biodegradable (i.e., they are readily degradable through the action of water and/or microorganisms.), their widespread use has been hindered by their high cost of production. The manufacture of alpha hydroxy acid polymers and copolymers has been costly in large part because of the difficult process by which they have been made heretofore.
The polymerization of lactide (3,6-dimethyl-1,4-dioxane-2,5-dione) and glycolide (1,4-dioxane-2,5-dione) which are composed of two units of lactic or glycolic acid in the form of a ring, respectively is, of course, well known. In this polymerization process, the ring monomers and any comonomers present are heated together in the presence of a ring opening catalyst such as stannous octoate, or a compound of yttrium or a lanthanum series rare earth catalyst or a titanate. However, extremely low polymerization rates and the resultant long reaction times have made continuous process for making these polymers substantially impractical from an industrial point of view. On the other hand, the use of batch reactions for this purpose results in polymers having excessively high melt viscosity and low melt stability. These, in turn, lead to polymer discoloration and low yields. Such problems have contributed to making these potentially important polymers too expensive for widespread use in consumer applications. Problems have contributed to making these potentially important polymers too expensive for widespread use in consumer applications.